A clutch mechanism of the kind set out above is described in the specifications of French published patent application No. FR 2 585 424A and U.S. Pat. No. 4,751,991. In the latter, the said assembly means comprise, firstly an annular component called a crown ring, frusto-conical in shape and arranged on the side of the diaphragm opposite to the cover plate, and secondly a plurality of retaining lugs, which are relatively thin and which are flat. These retaining lugs are integral with the cover plate and pass axially through the diaphragm. Near to the free end of each of these retaining lugs, a locating bend is formed, with the crown ring bearing axially on the locating bends of the lugs. The diaphragm is thus mounted pivotally, with a resilient biassing action, between a primary abutment, carried by the cover plate, and a secondary abutment which is carried by the crown ring and which is aligned in facing relationship with the primary abutment.
For the assembly of such a clutch mechanism, the retaining lugs are initially straight, extending parallel to the axis of the assembly. The diaphragm and the crown ring are fitted over the free ends of these straight lugs, and these ends are then bent outwardly in order to form the locating bends mentioned above. For this reason, each of the retaining lugs is formed with a groove to define a line of bending, and this groove presents a local reduction in the thickness of the lug.
This arrangement is generally satisfactory, but the crown ring can sometimes become accidentally lodged or jammed in one or more of these grooves. As a result, after the bending of the lugs to form the locating bends, the crown ring then becomes held by the groove or grooves in which it is engaged, and as a consequence loses the desired freedom of movement which it needs in order that the diaphragm can pivot easily.
In addition, a substantial biassing force may occur, tending to restrain the diaphragm against its pivoting movement between the primary and secondary abutments. This restraint gives rise to parasitic frictional effects during the pivoting movement of the diaphragm, and some deformation of certain of the retaining lugs may be necessary in order to produce a variation in the spacing between the primary and secondary abutments when the diaphragm is pivoting.
The engagement surface which is offered by the crown ring to the diaphragm may also be reduced under these conditions. Thus there can arise a non-uniform pressure distribution at the level of the diaphragm when, for example, the crown ring becomes engaged in some of the grooves in the retaining lugs and not in others.
In order to overcome these drawbacks it has already been proposed to make technical changes and to modify the method of assembly, for example by modifying the cover plate, but always in ways that are expensive. This leads to a loss of the advantages which are obtained by the specific configuration of the cover plate.